Double debit

I have been struggling to get multichoice to refund me my money they over charged me. I was debited 1600.00 for a family and compact plus subscription. Their explanation is that there was a decoder that was activated by their system, but they are refusing to refund me and sending me from pullar to post I have 3 case numbers that they 'opened for investigation' with no feedback. Am really ****ed off at this.